A motor vehicle fuel filter includes a filter housing and a drainage device wherein the drainage device includes a collecting cup, a fastening screw for the collecting cup, as well as a threaded part secured in the filter housing and including an inner thread for receiving the fastening screw. On the exterior of the threaded part at least one drainage passage extends from the interior of the filter housing into the collecting cup.
Filters for liquids have often in addition to their primary filtering function also the task of acting as a water separator. In particular in case of fuel filters of motor vehicles, the filter housing is provided for this purpose with a drainage device for removing water that has collected. In this connection, the higher specific gravity of water relative to fuel is utilized in order to collect the entrained water at the bottom of the filter housing, in the direction of gravity, and to guide it by means of a drainage device to a collecting cup.
WO 2005/079949 A1 discloses such a filter in which at the bottom side of the filter housing a collecting cup threadably attached or screwed on by means of a central fastening screw. The filter housing has at its bottom end, relative to the force of gravity, a threaded part with an inner thread for receiving the fastening screw. The threaded part is embodied as a block with square cross-section and is positioned on radially inwardly projecting noses of a securing element that has a round cross-section. The securing element is provided with tabs that are bent about the parallelepipedal threaded part and thus positionally secure the threaded part. The assembly of the round securing element and the parallelepipedal threaded part is inserted into the bottom end of the filter housing and, in the inserted state, is ready for receiving the fastening screw of the collecting cup. Between the circumferential surfaces of the threaded part arranged in a square and the receptacle of circular cross-section, there are drainage passages formed on the exterior of the threaded part; these drainage passages have the shape of a segment of a circle and extend from the interior of the filter housing into the collecting cup and enable drainage of water from the interior of the filter housing into the collecting cup.
In this connection, the high constructive expenditure is disadvantageous in that, in addition to the filter housing, two components, i.e., the round securing element and the parallelepipedal threaded part are required and that the threaded part must be secured in a complicated way by bending the securing tabs. In particular, the tightening forces of the fastening screw and also other external force effects can cause local stress peaks at the noses of the receptacle where the threaded part is resting. An accidental eccentric loading can also lead to stress in the corner area of the parallelepipedal threaded part which corner area has no or at most a linear contact surface on the circumferential wall of its receptacle. A thin-walled construction of the filter housing, in particular made from plastic material, is therefore not possible or possible only with limitations.
Thus, the need exists to provide a filter of the aforementioned kind configured in such a way that the attachment of the collecting cup on the filter housing is improved with regard to carrying capacity and liquid flow rate.